1. Field of the Invention
The present invention relates to a sputtering target of a single crystal aluminum alloy which is set in a sputtering apparatus and used in the formation of a thin film, and a method for producing the same.
2. Description of the Related Art
A sputtering process comprises irradiating a sputtering target by an ion beam under reduced pressure, impacting the ions on a target surface to evaporate a material of the target, and depositing the material on a substrate to form a thin film of the material. The sputtering process is widely used for forming the thin film, and targets containing various elements are used for the improvement of properties of the formed thin films.
In the sputtering process, crystal orientations on the surface and in an interior of the target are known to have great influences on emitting properties of atoms from the target and, in turn, have influences on film forming properties such as a film formation speed and step coverage of the thin film formed on the substrate (cf. Phys. Rev., 102, 699 (1956)). Therefore, it is important to control the crystal orientations of the target for the formation of the thin film with good film properties.
Hitherto, a polycrystalline aluminum alloy has been used as a material for a sputter target, the crystal structure and orientations of which are adjusted by working or heat treating it. But, since this target consists of a polycrystalline alloy, it is impossible to fully control the crystal orientations in accordance with purposes of the use.
For the production of a single crystal material having controlled crystal orientations, there are known solidifying methods such as the Bridgeman method, the Charmars method and the Czochralski method. However, in a case of an alloy, a solute suffers from a solid-liquid separation during solidification, and added elements are segregated to provide a nonuniform distribution of elements in these solidifying methods.
For example, when an eutectic element such as Cu or Si is added to aluminum, the concentration of such an alloy element in a solid phase is lower than that in a liquid phase during the solidification, so that, with the progress of solidification, the alloy element is concentrated in the liquid phase, whereby the concentration of the alloy element in the liquid phase is increased. By the influence of such concentration change, the concentration of the alloy element in the solid phase increases from the initial part to the ending part of the solidification.
When a peritectic element such as Ti or V is added to aluminum, a phenomenon contrary to the above appears. Then, only a single crystal having a nonuniform distribution of the added element is obtained, and such a single crystal is not suitable for a sputtering target material.
The above phenomena are significant, particularly when the diameter or longitudinal size of the target which can be set in the sputtering apparatus is 100 mm or larger. Accordingly, there has not been known any sputtering target of a single crystal aluminum alloy having a uniform distribution of an added element.